An effector is a kind of hardware that allows a user to experience a virtual reality, i.e., a device that stimulates human senses to create a feeling of presence in a virtual world. That is, a motion effector or a motion simulator allows a user, sitting on an entertainment chair fixed but moving in synchronism with varying scenes projected on a full-sighted screen, to feel real while he or she, watching the screen, is stirring, shifting or rotating the entertainment chair.
Such movement of the entertainment chair may be driven by a hydraulic mechanism which works under the control of a motion effector controller.
A schematic diagram of a conventional motion effector 100 is given in FIG. 1 and details of the plant 140 shown in FIG. 1 are shown in FIG. 2.
The conventional motion effector 100 comprises: a reference provider 110, a subtractor 120, a PID (proportional integral derivative) controller 130 and a plant 140.
The reference provider 110 serves to feed a reference input R(t) which is an electrical signal reflecting a desired movement of the entertainment chair. The subtractor 120 produces an error signal E(t) by subtracting an output signal Y(t) from the reference input R(t). As a controller or compensator, the PID controller 130 manipulates the error signal E(t) so as to produce a control signal U(t). The plant 140 has a moving part therein including the entertainment chair; and is the target of the control by the motion effector controller.
FIG. 2 illustrates details of the plant 140 shown in FIG. 1. The plant 140 includes: a first AMP (amplifier) 141, a hydraulic mechanism 142 used as an actuator, a motion simulator 143, a sensor 144 and a second AMP 145.
The first AMP 141 magnifies the intensity of the control signal U(t) to a proper level to be used to control the hydraulic mechanism 142. The hydraulic mechanism 142 has therein hydraulic pumps, valves and a reservoir (which are not shown) for use in driving the motion simulator 143. The motion simulator 143, presented as the entertainment chair herein, is made to move according to the operation of the hydraulic mechanism 142. The sensor 144 detects the movement of the motion simulator 143 to generate an electrical signal reflecting the detected movement of the motion simulator 143. The electrical signal is finally used in the feedback as illustrated in FIG. 1 after being amplified at the second AMP 145.
The operation of the conventional motion effector 100 will now be described.
The error signal reflecting the difference between the reference input R(t) representing the motion that the motion simulator 143 is expected to make and the output signal Y(t) fed back from the plant 140 to the subtractor 120 is provided to the PID controller 130. So as to compensate the error between the reference input R(t) and the output signal Y(t), the error signal E(t) is manipulated at the PID controller 130 and then transformed into the control signal. The control signal produced at the PID controller 130 is a function of the error signal E(t) and represented by: ##EQU1##
wherein, K.sub.P, K.sub.D and K.sub.I are a proportional gain, a differential gain and an integral gain, respectively.
The control signal U(t) is applied to the hydraulic mechanism 142 to be used in controlling the hydraulic mechanism 142 after undergoing an amplification at the first AMP 141. The hydraulic mechanism 142 drives the motion simulator 143 in such a manner that the motion simulator 143 incessantly traces the desired movement represented by the reference input R(t) under the control of the PID controller 130. The sensor 144 transforms the movement of the motion simulator 143 into an electrical signal. The output signal Y(t) produced as a result of applying the control signal U(t) is used in the subtraction at the subtractor 120 to thereby produce the error signal E(t). Continuous feedbacks enable the PID controller 130 to finally control the movement of the motion simulator 143 to thereby trace the desired movement.
Albeit popular, however, the PID controller 130 has inherent deficiencies to be used in the motion effector: it provides little countermeasure against the time gap between the reference input R(t) and the output signal Y(t), which may lessen the sense of reality of the user; and, further, such factors as external disturbances, modeling errors, sensor noises, etc. cannot be fully considered and compensated by using the PID controller 130.
Accordingly, there has existed a need to develop a controller capable of provicing a higher degree of sense of reality to the user.